It is well known that pulmonary arterial hypertension in congenital heart disease is an important prognostic factor, as is pulmonary vascular resistance. So it is tempting to get certain radiologic index that could predict the presence and the degree of pulmonary arterial hypertension. A total of 152 cases of left to right shunt with pulmonary arterial hypertension and 50 cases of left to right shunt without pulmonary arterial hypertension is presented, in which cardiac catheterization and angiiocardiography were done at the Department of Radiology, Seoul National University Hospital between March 1981 and February 1983. Statistical analysis of plain radiographic findings with the emphasis on the correlation of radiologic index with the hemodyanmic data. The results are as follows; 1. The incidence of pulmonary arterial hypertension is much less in atrial septal defect than other two disease groups of left to right shunt. 2. PA/T ratio correlates well with pulmonary arterial pressure (r=0.674), especially in mild pulmonary hypertension group. No correlation in moderate pulmonary hypertension group in significant level 3. PA/T ratio is below 38 in total cases of normal control group and in 32 cases (21.0%) among 152 cases of pulmonary arterial hypertension group. 4. The average PA/T ratio in normal pressure group of left to right shunt is 35.3 which has no significant difference from that of normal control group. 5. The average CT ratio of pulmonary arterial hypertension group is 59.0 which is larger than 49.1 of normal control group. The CT ratio shows no correlation with the pulmonary arterial pressure in statistically significant level. 6. The higher the pulmonary arterial pressure, the larger th eRp/Rs value, The Ps/Rs in atrial septal defect is 0.1393 in average, the lowest value in comparison with other two disease groups.